You can work on a colleague’s animation from time to time, and depending on the circumstances, you'll handle it differently.
Typically, it can be very frustrating to work on someone else's file. Animators have different methods and workflows that they incorporate in their process. Sometimes you will get a file and when you analyze it, it makes perfect sense to you. Other times you may be left in absolute confusion trying to decipher the animator’s thought/work process.
The former can be relatively easy to work with if their workflow closely resembles your own, so changes should go smoothly.
The latter, however, can cause you to go gray overnight and utter countless curses on the file’s creator. In this case, I will strip out everything but the key poses and maybe some breakdowns to maintain the essence of the animation and rebuild it. I find that this saves me oodles of time and countless hours on the therapist's couch.